Components for aerospace, automotive and like service applications have been subjected to the ever increasing demand for improvement in one or more mechanical properties, such as tensile strength, ductility, high or low cycle fatigue life, resistance to impact damage, etc. while at the same time maintaining or reducing the weight of the component. To this end, the Charbonnier et al U.S. Pat. No. 4,889,177 describes a method of making a composite casting wherein a molten lightweight alloy, such as aluminum or magnesium, is countergravity cast into a gas permeable sand mold having a fibrous insert of high strength ceramic fibers positioned therein by metallic seats on the mold cavity wall so as to be incorporated into the casting upon solidification of the molten alloy.
The Funatani et al U.S. Pat. No. 4,572,270 describes a method of making a composite casting to this end wherein a mass of high strength reinforcing material, such as fibers, whiskers, or powder, is incorporated into a lightweight matrix metal, such as aluminum or magnesium, that is die cast around the reinforcing mass in a pressure chamber.
A technique commonly referred to as bicasting has been employed to improve one or more mechanical properties of superalloy castings used as aerospace components. Bicasting involves pouring molten metal into a mold cavity in which a preformed insert is positioned in a manner to augment one or more mechanical properties in a particular direction(s). The molten metal surrounds the insert and, upon solidification, yields a composite casting comprising the insert embedded in and hopefully soundly bonded with the solidified metal without contamination therebetween. However, as described in U.S. Pat. No. 4,008,052, attempts at practicing the bicasting process have experienced difficulty in consistently achieving a sound metallurgical bond between the insert and the metal solidified therearound without bond contamination. The inability to achieve on a reliable basis a sound, contamination-free bond between the insert and the cast metal has significantly limited and, with some material systems, eliminated use of bicast components in applications, such as aerospace components, where reliability of the component in service is paramount.
It is an object of the invention to provide an improved bicasting type of process for making a casting wherein a sound, uncontaminated, void-free, metallurgical bond is reliably produced between the preformed insert and the solidified metal therearound.